[PATCH v3 21/35] x86/bugs: Determine relevant vulnerabilities based on attack vector controls.

David Kaplan
2025-01-08T20:25:52Z

The function should_mitigate_vuln() defines which vulnerabilities should
be mitigated based on the selected attack vector controls. The
selections here are based on the individual characteristics of each
vulnerability.

Signed-off-by: David Kaplan <david.kaplan@amd.com>
---
arch/x86/kernel/cpu/bugs.c | 69 ++++++++++++++++++++++++++++++++++++++
1 file changed, 69 insertions(+)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index 88eba8e4c7fb..175dbbf9b06e 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -347,6 +347,75 @@ static void x86_amd_ssb_disable(void)
wrmsrl(MSR_AMD64_LS_CFG, msrval);
}

+/*
+ * Returns true if vulnerability should be mitigated based on the
+ * selected attack vector controls
+ *
+ * See Documentation/admin-guide/hw-vuln/attack_vector_controls.rst
+ */
+static bool __init should_mitigate_vuln(unsigned int bug)
+{
+ switch (bug) {
+ /*
+ * The only spectre_v1 mitigations in the kernel are related to
+ * SWAPGS protection on kernel entry. Therefore, protection is
+ * only required for the user->kernel attack vector.
+ */
+ case X86_BUG_SPECTRE_V1:
+ return cpu_mitigate_attack_vector(CPU_MITIGATE_USER_KERNEL);
+
+ /*
+ * Both spectre_v2 and srso may allow user->kernel or
+ * guest->host attacks through branch predictor manipulation.
+ */
+ case X86_BUG_SPECTRE_V2:
+ case X86_BUG_SRSO:
+ return cpu_mitigate_attack_vector(CPU_MITIGATE_USER_KERNEL) ||
+ cpu_mitigate_attack_vector(CPU_MITIGATE_GUEST_HOST);
+
+ /*
+ * spectre_v2_user refers to user->user or guest->guest branch
+ * predictor attacks only. Other indirect branch predictor attacks
+ * are covered by the spectre_v2 vulnerability.
+ */
+ case X86_BUG_SPECTRE_V2_USER:
+ return cpu_mitigate_attack_vector(CPU_MITIGATE_USER_USER) ||
+ cpu_mitigate_attack_vector(CPU_MITIGATE_GUEST_GUEST);
+
+ /* L1TF is only possible as a guest->host attack */
+ case X86_BUG_L1TF:
+ return cpu_mitigate_attack_vector(CPU_MITIGATE_GUEST_HOST);
+
+ /*
+ * All the vulnerabilities below allow potentially leaking data
+ * across address spaces. Therefore, mitigation is required for
+ * any of these 4 attack vectors.
+ */
+ case X86_BUG_MDS:
+ case X86_BUG_TAA:
+ case X86_BUG_MMIO_STALE_DATA:
+ case X86_BUG_RFDS:
+ case X86_BUG_SRBDS:
+ return cpu_mitigate_attack_vector(CPU_MITIGATE_USER_KERNEL) ||
+ cpu_mitigate_attack_vector(CPU_MITIGATE_GUEST_HOST) ||
+ cpu_mitigate_attack_vector(CPU_MITIGATE_USER_USER) ||
+ cpu_mitigate_attack_vector(CPU_MITIGATE_GUEST_GUEST);
+ /*
+ * GDS can potentially leak data across address spaces and
+ * threads. Mitigation is required under all attack vectors.
+ */
+ case X86_BUG_GDS:
+ return cpu_mitigate_attack_vector(CPU_MITIGATE_USER_KERNEL) ||
+ cpu_mitigate_attack_vector(CPU_MITIGATE_GUEST_HOST) ||
+ cpu_mitigate_attack_vector(CPU_MITIGATE_USER_USER) ||
+ cpu_mitigate_attack_vector(CPU_MITIGATE_GUEST_GUEST) ||
+ cpu_mitigate_attack_vector(CPU_MITIGATE_CROSS_THREAD);
+ default:
+ return false;
+ }
+}
+
+
/* Default mitigation for MDS-affected CPUs */
static enum mds_mitigations mds_mitigation __ro_after_init =
IS_ENABLED(CONFIG_MITIGATION_MDS) ? MDS_MITIGATION_AUTO : MDS_MITIGATION_OFF;
--
2.34.1